Recently, efforts have been directed towards the development of integrated data, voice, and video communications systems. In response to this demand, a new communications protocol known as Isochronous Ethernet (IsoEthernet) has been proposed by the Institute of Electrical and Electronic Engineers as an addition to IEEE Standard 802.9. IsoEthernet is a scheme for multiplexing the combination of a conventional Ethernet channel of approximately 10 Mb/sec and 96 conventional B-channels onto a single standard wire pair in each direction. One end of the wire pair terminates in a "serving closet", which is used to provide an interface between the wire pair and a plurality of user devices such as computers, processors, and/or telephone equipment. An interface is required for the purpose of directing incoming signals on a first wire pair to the appropriate user device, and also for transforming outgoing signals produced by user devices into signals which are to be transmitted on a second wire pair.
One feature common to current state-of-the-art IsoEthernet systems is that these systems are directed to providing separate treatment for Ethernet channels and B-channels. For example, an Ethernet channel may be separated from a B-Channel set by a demultiplexer and directed to a standard Ethernet multiport repeater or a local area network (LAN) switch. These repeaters may be conceptualized as active electrical terminal blocks which connect various ports together into a single shared bandwidth media of 10 Mb/sec. Ethernet repeaters and LAN switches are currently used in a wide variety of LAN applications, but these devices are not traditionally used to switch real-time voice and video signals. These real-time signals, carried by B-Channels, are handled in accordance with standard telephony practices. For example, the B-channels are typically configured in a TDM (time-division multiplex) arrangement, and may be used to provide dedicated service to a plurality of voice or video real-time communications devices. The B-Channels are switched using conventional PBX or PBX-like structures. To handle 96 B-Channels, a relatively expensive 6.144 mHz.times.N (where N=number of ports) switch is utilized in current state-of-the-art systems. PBX structures are arranged to handle a relatively large number of narrow bandwidth channels, and are not the apparatus of choice for implementing local area networks, which typically involve wide-bandwidth data signals communicated during relatively brief time intervals. In the typical ISDN B-Channel scheme, the B-Channel is generally used to carry an FDX 64 kb/s voice circuit. However, the ISDN B-Channels could be used to carry video, data or a combination of voice, video, and data. DS1 is a TDM system having a 1.544 Mb/sec transmission, i.e.. 24 8-bit channels and 24 framing bits. Each channel is 8 kHz.times.8=64 Kb/sec. All 23 B-Channels of a DS1 signal can be data. i.e., 23.times.64 Kbits.
FIG. 1 is a block diagram of a prior art communication system 400 topology which provides data and voice/video communications to and from a plurality of endpoint devices using IsoEthernet communication protocols. In the system of FIG. 1, the endpoint devices are provided in the form of work stations 411. Each work station 411 includes telephone equipment 401 and a personal computer 403. The term "telephone" is to include any real-time communications functions such as voice, video, or conference control and data. The telephone equipment 401 included in a specific work station 411 connects to a B-Channel trunk providing a dedicated set of 96 B-Channels. In this manner, each work station 411 is provided with a separate, dedicated B-Channel trunk, such as a first set of 96 B-Channels 402, a second set of 96 B-Channels 405, or a third set of 96 B-Channels 408.
The first set of 96 B-Channels 402 is coupled to a multiplexer/demultiplexer (MUX/DEMUX) 447. Similarly, the second set of 96 B-Channels 405 and the third set of 96 B-Channels are each coupled to corresponding MUX/DEMUX 447. Each MUX/DEMUX 447 combines a set of 96 B-Channels with a 10 Mb/sec Ethernet channel. For example, the first set of 96 B-Channels 402 is combined with Ethernet Channel 404, the second set of 96 B-Channels 405 is combined with Ethernet Channel 407, and the third set of 96 B-Channels 408 is combined with Ethernet Channel 410. Each MUX/DEMUX 447 combines an Ethernet channel and a set of 96 B-Channels to provide a 16 Mb/sec IsoEthernet channel 409 from the work station to the serving closet. The same (symmetric) function is also provided from the closet to the work station.
The IsoEthernet channels 409 are routed to a serving closet 475, which may be situated in a remote location with respect to work stations 411. At the serving closet 475, a demultiplexer (MUX/DEMUX) 477 is applied to each 16 Mb/sec IsoEthernet channel 409 to separate the IsoEthernet channel 409 into a 10 Mb/sec Ethernet channel and a B-Channel set of 96 B-Channels. The 10 Mb/sec Ethernet channels are routed to an Ethernet hub 415, and the B-Channel sets are routed to a TDM bus 423. The Ethernet hub may typically be a classical multiport repeater or a LAN switch. TDM bus 423 is controlled by a TDM system controller 417 which implements time-division multiplexing.
The operational speed of TDM system controller 417 is determined by the number of work stations 411 and/or quantity of telephone equipment 401 utilized in a given communications system. For example, in the system of FIG. 1, three work stations 411 are shown, each requiring a dedicated set of 96 B-Channels. Each set of B-Channels operates at approximately 6 Mb/sec, and the TDM system controller 417 must be equipped to switch three sets of B-Channels. Therefore, the TDM system controller 417 must have a switching speed of 18 Mb/sec. If twelve work stations 411 were present, the required switching speed would be 72 Mb/sec. Using current state-of-the-art technology, a 72-mHz switch is significantly more costly than an otherwise comparable 6-mHz switch. As the number of work stations 411 is increased, the requirements imposed on the TDM system controller 417 switching speed are increased proportionally. Therefore, systems employing a moderate to high number of work stations 411 may be rendered expensive and/or infeasible. It would be desirable to have a system topology where work stations 411 may be added to the system without having to increase the operational speed of TDM system controller 417.
The TDM system controller 417 is coupled to a digital trunk interface module 419 which interfaces the TDM system controller 417 with a conventional telephone system switch 449. The digital trunk interface module 419 communicates with the conventional telephone system switch 449 using a standard protocol such as PRI (Primary Rate Interface), BRI (Basic Rate Interface), T1, E1, DS3, or the like. Each personal computer 403 is connected to a corresponding Ethernet channel, such as Ethernet channel 404. Ethernet channel 407, or Ethernet channel 410. Each Ethernet channel 404, 407, 410 is routed to a corresponding MUX/DEMUX 447.
Existing IsoEthernet system topology is not especially well-suited to the needs of certain users. Small businesses generally have no need for 96 dedicated real-time B-Channels per user, and it is even quite unlikely that an entire small business will require a total of 96 B-Channels. With the increasing sophistication of user equipment, it would be desirable to dynamically allocate the B-Channels, based upon the immediate needs of the system users at a given point in time. It would be advantageous to change B-Channel allocation in a given system to adapt to changing system requirements and user demand.